Variations from the Anomalous X - Ray Pulsar 4 U 0142 + 61

We report on our Spitzer observations of the anomalous X-ray pulsar 4U 0142+61, made following a large X-ray burst that occurred on 2007 February 7. To search for mid-infrared flux variations, four imaging observations were carried out at 4.5 and 8.0 μmwith the Infrared Array Camera from February 14 to 21. No significant flux variations were detected, and the average fluxes were 32.1±2.0 μJy at 4.5 μm and 59.8±8.5 μJy at 8.0 μm, consistent with those obtained in 2005. The non-detection of variability is interesting in light of reported rapid variability from this source in the near-infrared, but consistent with the fact that the source already went back to its quiescent state before our observations began, as indicated by contemporaneous X-ray observations. In order to understand the origin of the near-infrared variability, frequent, simultaneous multi-wavelength observations are needed. Subject headings: infrared: stars — pulsars: individual (4U 0142+61) — X-rays: stars — stars: neutron